<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <form name="form1">
        <h2>form1</h2>
        <p>
            <select name="city">
                <option value="nj">南京</option>
                <option value="sh">上海</option>
                <option value="wx" selected>无锡</option>
                <option value="sz">苏州</option>
            </select>
        </p>
    </form>
    <script>
        console.log(document.form1.city);
        console.log(document.form1.city.value);

        setTimeout(() => {
            document.form1.city.value = 'sz';
        }, 3000);



    </script>
</body>

</html>